An intervertebral foramen is an aperture extending generally laterally from the spinal canal dimensioned to accommodate the exiting nerve roots from the spinal cord at a given vertebral level in the spine. Within a single vertebral level, an intervertebral foramen is defined anteriorly by the annulus of the intervertebral disc and the posterior and lateral aspects of the adjacent superior and inferior vertebral bodies, superiorly by the pedicle of the superior vertebra, inferiorly by the pedicle of the inferior vertebra, and posteriorly by the facet joint formed by the inferior articulating facet of the superior vertebra and the superior articulating facet of the inferior vertebra. In a normal, non-pathologic spine, the intervertebral foramen is dimensioned such that the exiting nerve roots are adequately protected from compression and/or other undesirable contact during flexion, extension, lateral bending, and axial rotation of the particular vertebral level. This protection is provided by maintaining the volume of the intervertebral foramen during (or promptly restored after) such movements, as well as under the axial loading that occurs at that vertebral level during activities of daily living.
The spatial integrity or volume of the intervertebral foramen may become compromised due to any of a number of events or pathologies, resulting in a constriction or narrowing of one or more aspects of the intervertebral foramen. These may include, but are not necessarily limited to, degenerative disc disease, disc failure or rupture due to trauma, osteophyte formation and/or calcification of the ligamentum flavum, intervertebral osteochondrosis, scoliosis, and/or destabilization from spine surgery procedures (e.g. discectomy, fusion, total disc replacement, nucleus replacement). When this occurs, the resulting narrowing or constriction (“lateral stenosis”) may cause the exiting nerve root to be compressed by one or more of the aspects that define the intervertebral foramen. Depending on the severity of the condition, this may cause any of a host of problems for the patient, including shooting pain (radiculopathy) and/or impaired motor or sensory nerve function due to the nerve compression. Moreover, the superior and inferior articulating facets may become misaligned (“facet imbrication”) and/or be undesirably compressed against one another, either condition which may be painful and/or adversely affect the proper function of the facet joint.
A variety of techniques have been developed over time for treating spinal pathologies, some of which have the effect of restoring the volume of the intervertebral foramen, but which may be limited by the path of nerve roots extending from the spine. Known techniques for example, do so indirectly through the use of procedures or implants in aspects of the spine remote to or outside of the intervertebral foramen. These procedures include, but are not necessarily limited to, the use of pedicle screw systems (fixed or dynamic) extending between adjacent pedicles, spinous process spacer systems positioned between adjacent spinous processes, plating systems (lateral and/or anterior) coupled between adjacent vertebral bodies, and intervertebral implants (e.g. fusion, total disc replacement, nucleus replacement) positioned between adjacent vertebral bodies. None of these systems or procedures restores the intervertebral foramen volume in a direct manner. Moreover, many of these procedures involve fusing or rigidly affixing the adjacent levels of the spine, such as via interbody fusion, posterior fusion, fusion via plating and/or fusion of the facet joint itself, each of which may limit normal physiologic motion.
A system capable of directly restoring the volume of an intervertebral foramen while not interfering with the path of nerve roots and other anatomical structures is therefore desirable.